In many genres of contemporary popular music (e.g. hip-hop, rap, techno, etc.), and in spite of the advent of digital audio media such as the compact disc and the MP3 computer audio file, the analog phonograph turntable still plays an integral role. In its simplest application, the turntable is used by a Disc Jockey (DJ) to play back, without manipulation, previously recorded phonograph records. A phonograph record is typically in the format of a vinyl record or is made from similar material. The record generally has the appearance of a twelve inch, 33⅓ rpm vinyl record with a spiral grove. In this scenario, the DJ simply places each successive phonograph record onto the turntable and initiates playback of the record by engaging the drive motor of the turntable and placing the stylus onto the record at the beginning of its groove trajectory.
This procedure is well known to anyone who has ever played a phonograph record. In more advanced applications, the DJ actually plays the turntable as a musical instrument. In this case, the DJ is not simply allowing the drive motor of the turntable to turn the phonograph record while the stylus traces through the groove trajectory of each selection on the record. Instead, the DJ manipulates the phonograph record itself, and various parts of the turntable mechanism, in order to dynamically change the rate at which the stylus passes through the groove trajectory of the record, the direction of the stylus' motion in the groove, and the position of the stylus within the groove trajectory. The development of subtle gestural techniques involving the analog phonograph turntable mechanism, often referred to as “scratching”, has given rise to a new musical art form: turntablism.
The system presented herein provides an accurate and robust means of transducing turntable “scratch” gestures into digital form. Once captured in digital form, the scratch gestures can be applied by client systems in almost limitless ways.
Several devices exist which allow a turntablist to control digital audio sources using a grooved vinyl record and a conventional DJ turntable equipped with standard tonearm and stylus. See US Patent Application Publication US 2002/0181378 by Bastian and U.S. Pat. No. 6,818,815, issued to Cohen. The grooved vinyl record which is used with these devices typically contains an audio recording of a “timecode signal”, or a “MIDI audio time code signal”. Timecode signals of different flavors have been widely used for many years in the film and broadcast industries, usually to synchronize motion picture film or video with an accompanying soundtrack recorded on another medium such as magnetic tape. However, the demodulation and decoding of these timecode signals is problematic under the conditions of turntable scratching, and devices based on the prior art have suffered from a lack of robustness and dependability.
For example, the modulation technique described in US 2002/0181378 and used by existing devices to encode “time code” onto vinyl, produces a signal which is modulated onto a single carrier frequency within the audio spectrum. Due to the quantity of information it carries, this single modulated “time code” signal is relatively wide in frequency width compared to the usable frequency spectrum of the vinyl record medium. This signal is therefore very vulnerable to noise degradation and distortions which are inherent in the vinyl record medium, especially when the vinyl discs on which this signal is recorded are subjected to a turntablist's repeated “scratching” of the disc.
Furthermore, the modulation techniques used by devices based on prior art to encode “time code” onto vinyl produce a sequence of modulated symbols which is causal with respect to the forward direction of turntable motion, hence demodulation of the “time code” values is generally not possible when the record is spinning in reverse. This detracts significantly from the usefulness of existing devices for turntablists seeking to capture the subtlest nuances of their performance. Finally, the existing devices do not allow the use of the vinyl phonograph record and turntable as a generalized velocity and position transducer for digital applications. They only allow the user to manipulate the playback of digital audio sources, and hence severely restrict the ultimate creative applications.
Several objects and advantages of the system presented herein are the following:
(a) To provide a system for accurately transducing velocity and position information into digital form for arbitrary and flexible use in digital systems, where said velocity and position information is transduced from a standard DJ analog phonograph turntable mechanism playing a special grooved vinyl record.
(b) To provide the system described in (a) such that accurate transduction of velocity and position information is maintained even under conditions of degraded signal quality resulting from heavy use of the special vinyl record.
(c) To provide the system described in (a) and (b) such that both velocity and absolute position information are equally recoverable whether the record is spinning in the normal forward direction of playback, or in the reverse direction.
(d) To provide the system described in (a)-(c) such that computational cost is kept low.
(e) To provide the system described in (a)-(d) such that no additional hardware beyond that which is commonly available to the DJ is required, excepting a modern digital computer equipped with stereophonic analog-to-digital converters. This keeps overall system cost to a minimum, and allows the user to freely configure their system to meet their own cost vs. quality requirements.